1. Field of the Invention
This invention relates to polyols and more particularly to a new three stage process for the preparation of polyols suitable for use in urethane foams.
2. Description of the Prior Art
Polyols suitable for use in urethane foams are usually made industrially by treating compounds very rich in hydroxyl with an alkylene oxide such as ethylene or propylene oxide, under alkaline catalysis, to give oxyalkylated products with moderate hydroxyl content. The compounds very rich in hydroxyl are usually obtained from either petroleum chemicals or carbohydrates, but the alkylene oxide is almost always derived from petroleum-based chemicals. Dependence on petroleum-based chemicals can be partially alleviated by making polyols by reaction of a compound very rich in hydroxyl, such as trimethylolpropane (TMP), with an agriculturally based fatty glyceride such as epoxidized tallow. This reaction can be carried out by heating with acid catalysts such as BF.sub.3 or HBr (J. Am. Oil Chemists' Soc. 51, 119-123 (1974); J. Am. Oil Chemists' Soc. 52, 289-292 (1975)). The TMP reacts in part with the glyceride linkages of the epoxidized tallow to give a mixture of mono- and diglycerides and fatty esters of TMP. The TMP also reacts at the oxirane linkages of the epoxidized tallow to give rise to fatty hydroxy ethers of TMP. The reaction mixture is a mixture of polyalcohols of moderate hydroxyl content and appropriate plasticizing character for good quality rigid urethane foams on reaction with an appropriate isocyanate and a blowing agent. Unfortunately, some of the TMP fails to react either at glyceride or oxirane function and consequently forms a second phase which solidifies out on standing at room temperature. Although, in the laboratory, most of the unreacted TMP can be eliminated by water-washing a solution of the polyol in a hydrocarbon solvent, the necessity of such a step would be a stumbling block to commercial adoption of the process.